The green form of ‘Glenodinium sanguineum Marchesoni' sensu Baldi was investigated in detail by light microscopy, scanning electron microscopy, transmission electron microscopy and by analysis of the SSU- and LSU rDNA genes. These data demonstrated it to be different from the red form of ‘G. sanguineum' (now Tovellia sanguinea) and to represent a new species, Baldinia anauniensis gen. et sp. nov. It lacked thecal plates and an apical groove, and was characterised by the presence of a peculiar lamellar body similar to that described from certain dinoflagellates harbouring a diatom endosymbiont. However, B. anauniensis had a typical dinoflagellate chloroplast, and pigment analysis by high-performance liquid chromatography revealed peridinin as the major carotenoid pigment. Phylogenies based on either SSU or LSU rDNA revealed a relationship to suessialoid and woloszynskioid lineages rather than to the diatom-containing species, though morphological support for this relationship could only be argued by the absence of trichocyst and to some extent the intraplastidial eyespot type. A ventral fibre attached to the right side of the longitudinal basal body, an arrangement not observed in any other dinoflagellate before. Numerous food vacuoles with cryptophyte remnants demonstrated that B. anauniensis was mixotrophic.